Numerous compositions for lubricating aluminum alloy materials are known in the prior art. However, there is still a need for aluminum alloy preforms which are lubricated before use and which also have good lubricity, cleanability and wettability properties. The term "lubricity" means the ability of a lubricant to maintain its film strength after aging and also after coming into contact with water. "Cleanability" means the ability to remove the lubricant from the finstock surface readily, preferably by rinsing with water. "Wettability" means the ability to cause spreading of water droplets as measured by contact angle.
As used herein, the term "preform" refers to an aluminum alloy body in any of several different unfinished and semi-finished forms. The term includes but is not limited to aluminum alloy rod bar, rolls, sheet, plate, ingots, castings, and extrusions.
In present industrial practice, most aluminum alloy preforms are lubricated with oil or emulsions at the time of shaping into final products. Consequently, the products must often be degreased after being formed. Degreasing requires an organic solvent such as trichlorethylene, which itself poses hazards to the health and safety of workers, as well as increased handling and transportation costs in disposal to assure the avoidance of environmental pollution.
Proposals have been made to reduce the problems noted above by lubrication with a lubricating oil dissolved in a volatile solvent. After the preform is shaped into a product or allowed to stand for some time the solvent evaporates, leaving residual oil on surface portions. Such residual oil is difficult to remove other than with volatile organic solvents and, if left on the product, provides an oily surface which can interfere with efficient operation later. The evaporated organic solvents may also cause unacceptable emission problems.
The need for lubrication of aluminum alloy preforms arises in several different metalworking operations, including but not limited to drawing, ironing, punching, stamping, rolling, and forging. Such operations require lubrication at an interface between the preform and a forming tool in order to reduce friction and minimize wear on the tool. As used herein, the term "forming tool" encompasses various types of apparatus employed in working aluminum alloys, including dies, ironing rings, punches, stamping tools, rolls, and forging presses.
Although lubricated preforms may be employed in many different contexts, the need is most acute in the manufacture of heat exchanger fins from aluminum alloy finstock provided with hydrophilic coatings. Several processes for producing hydrophilic coatings on aluminum alloy finstock are known in the prior art. Some references disclosing hydrophilic finstock coatings are Kaneko et al U.S. Pat. No. 4,421,789; Uchiyama et al U.S. Pat. No. 4,462,842; Imai et al U.S. Pat. No. 4,588,025; Kaneko et al U.S. Pat. No. 4,726,886; Sako et al U.S. Pat. Nos. 4,783,224 and 4,954,372; Mizoguchi et al U.S. Pat. No. 4,957,159; and Yamasoe U.S. Pat. No. 4,973,359. These finstock coatings perform satisfactorily in preventing accumulations of water droplets which might increase resistance to air flow adjacent the fins and thereby reduce heat exchange efficiency. However, it has been found that coated finstock also increases wear rates on forming dies which shape the finstock into heat exchanger fins. Attempts to reduce wear on the forming dies by lubrication with a conventional oil-base lubricant result in a need to degrease the shaped fins so that they may benefit from their hydrophilic coating. Accordingly, there is a need for a suitable lubricant composition which will reduce wear rates on the forming dies to satisfactory levels.
Courval U.S. Pat. No. 4,928,508 has proposed lubricating hydrophilic aluminum alloy finstock with a water-soluble lubricant coating that is dried before shipping and storage. The preferred water-soluble lubricant is an ethoxylated castor oil having some solubility in water. However, because of the limited solubility of ethoxylated castor oil in water, cleanability of fins made from the finstock may not be assured. In addition, the Courval lubricant composition is dissolved in isopropanol for application to the finstock. Health and safety concerns require specialized procedures and equipment in the use of isopropanol and other alcoholic solvents with consequent increased costs.